Endocrine Control Female Reproduction 4

Question 1

What is the role sex hormone binding globulin (SHBG) in female reproduction?

Answer 1

• High affinity binding protein for estrogens and adrogens
  
  • androgens bind with higher affinity than estrogens
  • bound hormones considered biologically inactive
  • hormones that are free or loosely associated with albumin are biologically available
• Hepatic SHBG production increased by the following:
  
  • estrogen
  • thyroid hormone
• Production is decreased by the following:
  
  • androgens
  • obesity
  • insulin

Question 2

List the major peptides involved in female reproduction?

Answer 2

• Inhibin A and B
• Activin
• Follistatin

Question 3

What is the role of Inhibin A and B in female reproduction?

Answer 3

• Inhibits FSH release
• Inhibin A
  
  • present in both granulosa and theca cells
  • secreted by the dominant follicle
  • secreted by the corpus luteum
• Inhibin B
  
  • secreted by granulosa cells of small antral follicles
  • increases in response to FSH stimulation
  • feeds back to modulate FSH release
  • marker of gonadal reserve

Question 4

What is the role of activin in female reproduction?

Answer 4

• homodimer of inhibin beta-subunits
• synthesized by the pituitary and ovary
• stimulates FSH release by local autocrine/paracrine rather than endocrine actions
• most circulating actiin is likely bound to follistatin

Question 5

What is the role of follistatin in female reproduction?

Answer 5

• inhibits FSH release by binding and neutralizing activin
• acts locally to inhibit follicular growth
• autocrine/paracrine actions

Question 6

Discuss the following stages of female development: menarche, adrenarche, and adult female.

Answer 6

• Menarche
  
  • median age 12.6 in US
  • occurs about 2 years after breast budding
  • secular trend in age of menarche
  • occurs at earlier ages over the centuries
• Adrenarche
  
  • occurs between 6-8 years, prior to onset of puberty
  • development of adrenal zona reticularis - androgen secreting compartment of adrenals
  • results in secretion of adrenal androgen, DHEAS
  • leads to development of pubic and axillary hair
  • uncouple from gonadarche
• Adult female
  
  • menstrual cycle 21-35 days in length
  • cycle varies by no more than +/- 2 days

Question 7

List the phases of the menstrual cycle.

Answer 7

• Ovarian follicular development
• Follicular phase
  
  • early
  • mid
  • late
• Luteal phase

Question 8

Describe the events during ovarian follicular development.

Answer 8

• Gonadotropin-independent and regulated by intraovarian growth factors
• Maturation of antral follicles and ovulation with resumption of meiosis requires FSH and LH
• A single dominant follicle emerges from growing follicle pool 5-7 days after to start of menses
• Other growing follicles become atretic

Question 9

Describe the events during the follicular phase.

Answer 9

• Early follicular phase
  
  • FSH increase persists from of last cycle
  • dominant follicle is selected
  • LH pulse frequency begins to increase in absence of negative feedback of effects of E2 and progesterone
  • LH stimulates thecal cell T production, aromatized into E2 by adjacent granulosa cells of follicle
    
    • aromatase activity increases with FSH-stimulated follicular growth
    • Inhibin B increases follicular growth
• Mid follicular phase
  
  • increasing GnRH pulse frequency
  • synergizes with increasing ovarian E2 and inhibin B production
  • suppresses FSH release
• Late follicular phase
  
  • continued increase E2 production induces mid-cycle LH surge
  • induces ovulation of the dominant follicle
  • increased GnRH pulse frequency to ~1 pulse/hour

Question 10

Describe the events of the luteal phase.

Answer 10

• Period after ovulation, usually 14 days
• Post ovulatory follicle
  
  • lueinizes, forming corpus luteum
  • secretes progesterone and E2
  • feed back to slow GnRH pulse frequency
  • as frequency slows, FSH release selectively increases and LH decreases
    
    • stimulates follicular recruitment to the next cycle
    • progesterone production falls in the face of decreasing LH levels
    • without conception and hCG production, the embryo does not sustain the corpus luteum preogesterone production

Question 11

Describe the events that occur in the endometrium during the menstrual cycle.

Answer 11

• Proliferation
  
  • E2 or synthetic estrogens stimulate proliferation od endometrial, stromal, and epithelial cells
  • estrogens also induce expression of progesterone receptors
    
    • Ability of endometrium to respond to progesterone depends on estrogen induction of progesterone receptors
• Differentiation
  
  • Prgestins such as progesterone or synthetic progestins induce differentiation of the poliferative endometrium
  • P also prepares the endometrium for implantation of the embryo
• Menstruation
  
  • In the absence of hCH produced by the embryo, P and E2 production by the corpus luteum stops
  • this withdrawal of P and E2 leads to vasomotor changes in the endometrium and shedding of the endometrial lining

Question 12

Describe the events that occur during menopause.

Answer 12

• cessation of ovarian follicular activity
• mean age 51-52 years
• ovarian estradiol virtually ceases at menopause
• ovarian androgen production continues from some years afterwards
• Androgens, primarily androstenedione can be aromatized extragonadally into estrogen